Mechanism and Control of Antiferromagnetic Coupling in Fe/Fe3O4 Junctions

Abstract We analyzed the M-H loop observed for Fe 3 O 4 /bcc-Fe(001) junctions with thin insertion layers of Co or Mn by using several models that include bilinear and biquadratic coupling and twisting of magnetization near the interface. Both biquadratic and twisting of the magnetization are found to be important for explaining the M-H loop. To clarify the mechanism of antiparallel (AP) coupling in the Fe 3 O 4 /bcc-Fe junction, we performed first-principles calculations for junctions with and without extra Fe atoms on hollow sites of the spinel lattice at the interface. It was shown that parallel coupling is stable for junctions without extra Fe atoms whereas AP coupling becomes stable when the number of extra Fe atoms increases. The results suggest that magnetic frustration may occur when a nonuniform distribution of the extra Fe atoms exists at the interface.